CN111637599A - Method for dereferencing thermo-physical property constant in enthalpy value formula of room air conditioner - Google Patents

Method for dereferencing thermo-physical property constant in enthalpy value formula of room air conditioner Download PDF

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CN111637599A
CN111637599A CN202010512110.1A CN202010512110A CN111637599A CN 111637599 A CN111637599 A CN 111637599A CN 202010512110 A CN202010512110 A CN 202010512110A CN 111637599 A CN111637599 A CN 111637599A
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constant pressure
specific heat
heat capacity
vaporization
capacity
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孔繁海
刘健
王奎
杨雷
杜启行
刘汉阳
刘晓汉
李立顺
刘克林
郭小峰
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JIANGSU ZHONGKE KINGDA ELECTRONIC TECHNOLOGY CO LTD
Shandong Institute of Metrology
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JIANGSU ZHONGKE KINGDA ELECTRONIC TECHNOLOGY CO LTD
Shandong Institute of Metrology
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F11/00—Control or safety arrangements
    • F24F11/62—Control or safety arrangements characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M99/00—Subject matter not provided for in other groups of this subclass
    • G01M99/002—Thermal testing
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M99/00—Subject matter not provided for in other groups of this subclass
    • G01M99/005—Testing of complete machines, e.g. washing-machines or mobile phones
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G06F30/28—Design optimisation, verification or simulation using fluid dynamics, e.g. using Navier-Stokes equations or computational fluid dynamics [CFD]
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/08—Thermal analysis or thermal optimisation

Abstract

The invention discloses a method for valuing thermophysical property constants in an enthalpy value formula of a room air conditioner, which analyzes and researches three important process quantity valuation methods of constant pressure specific heat capacity of dry air, constant pressure specific heat capacity of vapor, latent heat of vaporization of water and the like in an enthalpy value calculation formula, substitutes measured values into corresponding formulas to calculate the constant pressure specific heat capacity of the dry air, the constant pressure specific heat capacity of the vapor and the latent heat of vaporization of the water, can reflect the actual capacity of a tested machine more truly, calculates the refrigerating capacity more scientifically, and can obtain more accurate experimental data than fixed values.

Description

Method for dereferencing thermo-physical property constant in enthalpy value formula of room air conditioner
Technical Field
The invention relates to an enthalpy value calculation formula of a room air conditioner, in particular to a method for dereferencing a thermophysical property constant in the enthalpy value formula of the room air conditioner.
Background
The indoor air enthalpy method is one of the most commonly used methods for measuring the cooling capacity of a room air conditioner, and the enthalpy of air refers to the adiabatic heat contained in air, and is generally based on the unit mass of dry air. Values of three important process quantities such as constant-pressure specific heat capacity of dry air, constant-pressure specific heat capacity of water vapor and latent heat of vaporization of water in the conventional enthalpy value calculation formula are constant values, for example, the enthalpy value calculation formula of humid air given by the energy efficiency measurement detection rule JJF1261.2-2017 of a common room air conditioner is as follows:
ha＝1.01t+Wn(2500+1.84t)
in the formula: t is the dry bulb temperature, DEG C; wnThe moisture content of air, kg/kg (dry air); 1.01 is the average constant pressure specific heat capacity of air, kJ/(kg. K); 1.84 is the average constant pressure specific heat capacity of steam, kJ/(kg. K); 2500 is the latent heat of vaporization of water at 0 ℃ kJ/kg.
As another example, the formula of sensible heat and latent heat is given in GB/T7725-2004 as follows:
φsci＝qmiCpa(ta1-ta2)/Vn(1+Wn) (1)
in the formula: phi is asciShowing the cold quantity, W; cpaIs 1005+1846Wn，J/(kg·K)；ta1，ta2Respectively indoor side return air temperature and indoor side supply air temperature at DEG C.
φlci＝Klqmi(Wi1-Wi2)/Vn(1+Wn) (2)
In the formula: phi is alciIs latent cold quantity, W; kl2470 (this value is the latent heat of vaporization at 15 ℃. + -. 1 ℃), kJ/kg; wi1The absolute humidity of the return air at the indoor side is kg/kg; wi2Supplying air to the indoor side in the absolute humidity of kg/kg; v'nSpecific volume of humid air at the measuring point, m3/kg。
As can be understood from the annotations of the parameters in the formulas (1) and (2), in GB/T7725-: the average constant pressure specific heat capacity value of the dry air is 1.005 kJ/(kg.K); the average constant pressure specific heat capacity value of the water vapor is 1.846 kJ/(kg.K); the latent heat of vaporization of the water is 2470kJ/kg when the value of the latent heat of vaporization of the water is 15 +/-1 ℃. The value of the enthalpy calculation formula is slightly different from the value of a common enthalpy calculation formula obtained by consulting the data in the prior art. Meanwhile, it is known through communication with other laboratories that different laboratories also differ in value, for example, some laboratories have the following values: h isa＝1.005t+Wn(2501+1.846t)。
GB/T7725-2004: the calculation of refrigerating capacity needs to use the enthalpy value h of indoor return aira1'AND' indoor side air supply enthalpy value ha2"these two process quantities, during the actual test, the indoor return air temperature is the temperature at the return air inlet of the machine under test, and is required to be controlled at a fixed value, for example: the temperature is 27 +/-0.3 ℃ under the working condition of rated refrigeration T1; the indoor side blowing air temperature is the air temperature blown out by the tested machine, and is different from the tested machine, and is mostly between 11 ℃ and 15 ℃. The values of the constant pressure specific heat capacity of dry air, the constant pressure specific heat capacity of water vapor and the latent heat of vaporization of water corresponding to different temperatures are different if the values are fixed according to the GB/T7725-2004 standardAnd substituting the fixed numerical value into the measured temperature to calculate, wherein three physical property constants corresponding to the measured temperature are inconsistent, and the capability of the measured machine cannot be accurately reflected.
Disclosure of Invention
The method is used for analyzing and researching three important process quantity value taking methods such as the constant pressure specific heat capacity of dry air, the constant pressure specific heat capacity of vapor and the latent heat of vaporization of water in an enthalpy value calculation formula aiming at the problems in the background art, provides a method for taking a thermophysical property constant value in an enthalpy value formula of a room air conditioner, and provides a more scientific and reasonable value taking method for improving the accuracy of a refrigerating capacity measurement result of the room air conditioner.
In order to achieve the purpose, the invention adopts the following technical scheme:
a method for dereferencing the constant of thermophysical property in enthalpy value formula of air conditioner in room includes such steps as choosing the symbol C for specific heat capacity of dry air at constant pressurep,BRepresents; the latent heat of vaporization of water is denoted by the symbol r; symbol C for average constant pressure specific heat capacity of water vaporp,CIs expressed in enthalpy value ha＝Cp,Bt+Wn(r+Cp,Ct), wherein:
Cp,B＝1.005KJ/(kg.K),
Cp,C＝-4×10-7t2+0.0001t+1.859，
r＝-1.5×10-3t2-2.278t+2500.5；
in the formula: t is the dry bulb temperature, DEG C; wnThe moisture content of air was kg/kg (dry air).
Compared with the prior art, the invention has the following beneficial effects:
the invention substitutes measured values into corresponding formulas to calculate the constant pressure specific heat capacity of dry air, the constant pressure specific heat capacity of water vapor and the latent heat of vaporization of water, can more truly reflect the actual capacity of a tested machine, can calculate the refrigerating output more scientifically, and can obtain more accurate experimental data than fixed values.
Drawings
FIG. 1 is a fitting curve diagram of specific heat capacity at constant pressure of water vapor according to the present invention.
Fig. 2 is a graph fitted with the latent heat of vaporization of water according to the present invention.
Detailed Description
In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.
The method for dereferencing the thermophysical property constant in the enthalpy value formula of the room air conditioner re-dereferencing three important process quantities of the constant pressure specific heat capacity of dry air, the constant pressure specific heat capacity of water vapor, the latent heat of vaporization of water and the like in the enthalpy value calculation formula.
1. Constant pressure specific heat capacity definition and fitting value
The specific heat capacity at constant pressure is the heat absorbed by a certain substance with unit mass with the temperature increased by 1K under the condition of unchanged pressure, is a thermodynamic parameter only related to the state of the substance, and is represented by a symbol CpExpressed, the unit is: kJ/(kg. K). In any process, the increase in specific thermodynamic energy per unit mass of ideal gas at 1K is equal to the value of its specific heat capacity at constant pressure, and the increase in specific enthalpy is equal to the value of its specific heat capacity at constant pressure.
The specific heat at constant pressure of wet air per unit mass is composed of the specific heat at constant pressure of dry air and the specific heat at constant pressure of water vapor, and Cp,BThe constant pressure specific heat of dry air is kJ/(kg. K); cp,CThe constant pressure specific heat of the steam is kJ/(kg. K).
Because the refrigerating capacity test process has only a operating mode, the requirement of environment humiture is invariable, and the temperature fluctuation can be ignored to the value of specific heat capacity, consequently need not calculate average constant pressure specific heat capacity again, can directly use the data in the experience table.
Inquiry air cooler[11]The specific heat capacity at constant pressure (standard atmospheric pressure) of dry air can be obtained, see table 1.
TABLE 1 constant pressure specific heat capacity of dry air
Temperature/. degree.C Specific heat capacity at constant pressure Cp,B/kJ/(kg·K)
0 1.005
10 1.005
60 1.005
70 1.009
90 1.009
100 1.009
As the ambient temperature of the refrigeration capacity test is within 60 ℃, the method can be obtained from the following table 1:
Cp,B＝1.005kJ/(kg·K)
inquiry "engineering thermodynamics[12]The specific heat capacity at constant pressure of the water vapor can be obtained (see table 2).
TABLE 2 specific heat capacity at constant pressure of water vapor
Temperature/. degree.C Specific heat capacity at constant pressure Cp,C/kJ/(kg·K)
0 1.859
100 1.873
200 1.894
300 1.919
400 1.948
500 1.978
Because the span of the given temperature points is too large, the temperature points which are commonly used in the experiment are all within 50 ℃, and the change range of the specific heat capacity at constant pressure is gradually increased along with the increase of the temperature from the table 2. In order to avoid the adverse effect of the high-temperature section data on the low-temperature section data during data fitting, only the first 3 points are selected for fitting, and the obtained fitting curve chart is shown in figure 1, and the formula is as follows.
Cp,C＝-4×10-7t2+0.0001t+1.859
2. Latent heat of vaporization definition and fitting values
Latent heat of vaporization, i.e., the amount of heat absorbed by a liquid substance per unit mass during vaporization, is constant. When the liquid is boiled and vaporized under a constant pressure, although it is heated, the temperature of the liquid does not rise, and the liquid and vapor always maintain a saturation temperature corresponding to the liquid surface pressure. According to the theory of molecular motion, the heat applied to the liquid during boiling is mainly used to overcome the attraction between liquid molecules and the surface tension of the liquid, and to increase the potential energy of the molecules (the distance between molecules increases from liquid to vapor), while the kinetic energy of vapor and liquid molecules is not increased. Obviously, this heat is not used to raise the temperature of the liquid, but is used to convert the liquid into a vapor, so that the temperature of the liquid remains constant during boiling. This heat is consumed in the vaporization of the liquid as latent heat. The heat absorbed by 1kg of saturated liquid at a given temperature, which is converted into vapor at the same temperature, is called latent heat of vaporization, or simply referred to as heat of vaporization, and is denoted by the symbol r, and the unit of latent heat of vaporization is kJ/kg.
Inquiry "engineering thermodynamics[12]The latent heat of vaporization of water at different temperatures can be obtained (see table 3).
TABLE 3 latent heat of vaporization of water
Temperature/. degree.C Latent heat of vaporization r/kJ/kg
0 2501
1 2498.6
2 2496.3
6 2486.8
10 2477.4
14 2467.9
20 2453.8
26 2439.6
35 2418.4
45 2394.5
55 2370.5
60 2358.4
65 2346.2
70 2333.8
75 2321.4
80 2308.9
85 2296.2
90 2283.4
95 2270.4
100 2257.2
110 2230.5
The data of table 3 were fitted and the resulting fitted curve is shown in fig. 2, with the following equation.
r＝-1.5×10-3t2-2.278t+2500.5
The resulting fit equations are summarized in Table 4.
TABLE 4 summary of fitting equations
Figure BDA0002528768180000051
Figure BDA0002528768180000061
In sum, the indoor air enthalpy value h of the air conditionera＝Cp,Bt+Wn(r+Cp,Ct)＝1.005t+Wn(-1.5×10-3t2-2.278t+2500.5+(-4×10-7t2+0.0001t +1.859) t). The invention substitutes measured values into corresponding formulas to calculate the constant pressure specific heat capacity of dry air, the constant pressure specific heat capacity of water vapor and the latent heat of vaporization of water, can more truly reflect the actual capacity of a tested machine, can calculate the refrigerating output more scientifically, and can obtain more accurate experimental data than fixed values.

Claims (1)

1. A method for dereferencing a thermophysical property constant in an enthalpy value formula of a room air conditioner is characterized by comprising the following steps of: symbol C for constant pressure specific heat capacity of dry airp,BRepresents; the latent heat of vaporization of water is denoted by the symbol r; symbol C for average constant pressure specific heat capacity of water vaporp,CIs expressed in enthalpy value ha＝Cp,Bt+Wn(r+Cp,Ct), wherein:
said C isp,B＝1.005KJ/(kg.K),
Said C isp,C＝-4×10-7t2+0.0001t+1.859
R-1.5 × 10-3t2-2.278t+2500.5。
CN202010512110.1A 2020-06-08 2020-06-08 Method for dereferencing thermo-physical property constant in enthalpy value formula of room air conditioner Withdrawn CN111637599A (en)

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BR0304449A (en) * 2003-10-03 2005-05-31 Reinaldo De Oliveira Sensitive Heat Removal / Recovery Equipment and System - rrcs
CN1664524A (en) * 2005-03-28 2005-09-07 杭州家和智能控制有限公司 Fan coil heat exchange quantity metering method by air side enthalpy potential method
CN101446939A (en) * 2008-12-09 2009-06-03 南京大学 Method for calculating theoretical number of plates of rectifying tower by Excel
CN107178871A (en) * 2017-05-09 2017-09-19 广东美的制冷设备有限公司 Air conditioner and its refrigerating capacity acquisition methods and computer-readable recording medium

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BR0304449A (en) * 2003-10-03 2005-05-31 Reinaldo De Oliveira Sensitive Heat Removal / Recovery Equipment and System - rrcs
CN1664524A (en) * 2005-03-28 2005-09-07 杭州家和智能控制有限公司 Fan coil heat exchange quantity metering method by air side enthalpy potential method
CN101446939A (en) * 2008-12-09 2009-06-03 南京大学 Method for calculating theoretical number of plates of rectifying tower by Excel
CN107178871A (en) * 2017-05-09 2017-09-19 广东美的制冷设备有限公司 Air conditioner and its refrigerating capacity acquisition methods and computer-readable recording medium

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